In small boats with water-jet propulsion apparatus, there is a possibility of injury to the hands of crew members or swimmers caused by the impeller or shaft of the propulsion apparatus when the hands are by any chance inserted into the drafting port of the apparatus. Furthermore, there is the possibility that dust or seaweed will intrude into the duct of the same apparatus. In order to prevent these disadvantageous features, it is necessary to provide a protecting device at the entrance of the drafting duct.
Heretofore, a grate has been provided at the entrance of the drafting duct as a protecting device. However, dust or other small items, such as rope or seaweed, frequently passes through the grate and is wound around the impeller shaft and the like regardless of the provision of the protecting device thereby impairing the efficiency of the propulsion system. When this occurs, the protecting device must be temporarily removed to permit cleaning of the impeller shaft. Normally, considerble manpower and time is required to remove and replace the protecting device.